Modern researches of mensuration structure, assortment and commodity structure of forest stands of different tree species and age groups show certain specific features which do not correspond to the regularities, which are modeled in the current assortment and commodity tables. And first of all, this concerns to beech stands as the main forest-forming tree species of the Ukrainian Carpathians. Therefore, the development of appropriate regulatory information materials, that would account for the regional and age peculiarities of growth and commodity structure of overmature beech stands is relevant. It was the first time that the structure of two-layer stands was modeled for the subsequent development of commodity tables. For this purpose, first there were modeled the theoretical lists of tree distribution and the second layer (has lower variance of trees by diameter compared to the first layer), and then the distribution of trees by diameter classes of the stand’s 1st layer was determined as the difference between the combined list and 2nd layer distribution. It is determined that the main feature of the development of precise standards for assessing the commodity structure of two-layer stands is the need for their subsequent recalculation in connection with the displacement of the average diameter of layers (by 16–24 cm) compared to the total average diameter of the stand (for example, if the average diameter of a stand is 32 cm, then the average diameter of the 1st layer is 52 cm and the average diameter of the 2nd layer is 16 cm). This offset has a rather complex relationship with the structure of the distribution of growing stock, since the stock of the corresponding categories of quality of stands, expressed in terms of volume of trees, is a cubic quantity that changes faster than the change in the mean diameter, which in turn depends on the square of the sum of trees’ cross sections in the stand.
over-mature stands, two-layer stands, commodity tables, statistical analysis, systematic errors